(1) Field of the Invention
The invention relates generally to the field of tv ratings monitoring devices and more particularly to devices to determine ratings on cable systems.
(2) Brief Description of the Prior Art
Prior cable systems, in order to bring to the home 100+ channels, have provided more than one cable because each cable's capacity was approximately 66 channels. In order for a ratings service to monitor these cable systems, the service provided monitors having two cable inputs and an internal A/B switch to select which cable was presently being viewed.
Newer cable systems have provided fewer channels and thus have included only one cable. Some of these services, in order to provide security for their premium programming services, have converters which can sense a DC signal, typically on the order of 16 volts, and switch from amplifiying one set of frequencies to another, one set having premium or pay per view programming and the other not.
Rather than design a whole new cable monitor for these newer switchable systems, it is desirable to adapt an existing monitor. However, the existing monitors have no means for sensing the DC switch signal, and further, may have circuit vunerability to such a DC signal.